kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 302 insertions, 0 deletions

diff --git a/lib/crypto/md5.c b/lib/crypto/md5.c
new file mode 100644
index 000000000..3d2b017a0
--- /dev/null
+++ b/lib/crypto/md5.c
@@ -0,0 +1,302 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * MD5 and HMAC-MD5 library functions
+ *
+ * md5_block() is derived from cryptoapi implementation, originally based on the
+ * public domain implementation written by Colin Plumb in 1993.
+ *
+ * Copyright (c) Cryptoapi developers.
+ * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
+ * Copyright 2025 Google LLC
+ */
+
+#include <crypto/hmac.h>
+#include <crypto/md5.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/unaligned.h>
+#include <linux/wordpart.h>
+
+static const struct md5_block_state md5_iv = {
+	.h = { MD5_H0, MD5_H1, MD5_H2, MD5_H3 },
+};
+
+#define F1(x, y, z) (z ^ (x & (y ^ z)))
+#define F2(x, y, z) F1(z, x, y)
+#define F3(x, y, z) (x ^ y ^ z)
+#define F4(x, y, z) (y ^ (x | ~z))
+
+#define MD5STEP(f, w, x, y, z, in, s) \
+	(w += f(x, y, z) + in, w = rol32(w, s) + x)
+
+static void md5_block(struct md5_block_state *state,
+		      const u8 data[MD5_BLOCK_SIZE])
+{
+	u32 in[MD5_BLOCK_WORDS];
+	u32 a, b, c, d;
+
+	memcpy(in, data, MD5_BLOCK_SIZE);
+	le32_to_cpu_array(in, ARRAY_SIZE(in));
+
+	a = state->h[0];
+	b = state->h[1];
+	c = state->h[2];
+	d = state->h[3];
+
+	MD5STEP(F1, a, b, c, d, in[0] + 0xd76aa478, 7);
+	MD5STEP(F1, d, a, b, c, in[1] + 0xe8c7b756, 12);
+	MD5STEP(F1, c, d, a, b, in[2] + 0x242070db, 17);
+	MD5STEP(F1, b, c, d, a, in[3] + 0xc1bdceee, 22);
+	MD5STEP(F1, a, b, c, d, in[4] + 0xf57c0faf, 7);
+	MD5STEP(F1, d, a, b, c, in[5] + 0x4787c62a, 12);
+	MD5STEP(F1, c, d, a, b, in[6] + 0xa8304613, 17);
+	MD5STEP(F1, b, c, d, a, in[7] + 0xfd469501, 22);
+	MD5STEP(F1, a, b, c, d, in[8] + 0x698098d8, 7);
+	MD5STEP(F1, d, a, b, c, in[9] + 0x8b44f7af, 12);
+	MD5STEP(F1, c, d, a, b, in[10] + 0xffff5bb1, 17);
+	MD5STEP(F1, b, c, d, a, in[11] + 0x895cd7be, 22);
+	MD5STEP(F1, a, b, c, d, in[12] + 0x6b901122, 7);
+	MD5STEP(F1, d, a, b, c, in[13] + 0xfd987193, 12);
+	MD5STEP(F1, c, d, a, b, in[14] + 0xa679438e, 17);
+	MD5STEP(F1, b, c, d, a, in[15] + 0x49b40821, 22);
+
+	MD5STEP(F2, a, b, c, d, in[1] + 0xf61e2562, 5);
+	MD5STEP(F2, d, a, b, c, in[6] + 0xc040b340, 9);
+	MD5STEP(F2, c, d, a, b, in[11] + 0x265e5a51, 14);
+	MD5STEP(F2, b, c, d, a, in[0] + 0xe9b6c7aa, 20);
+	MD5STEP(F2, a, b, c, d, in[5] + 0xd62f105d, 5);
+	MD5STEP(F2, d, a, b, c, in[10] + 0x02441453, 9);
+	MD5STEP(F2, c, d, a, b, in[15] + 0xd8a1e681, 14);
+	MD5STEP(F2, b, c, d, a, in[4] + 0xe7d3fbc8, 20);
+	MD5STEP(F2, a, b, c, d, in[9] + 0x21e1cde6, 5);
+	MD5STEP(F2, d, a, b, c, in[14] + 0xc33707d6, 9);
+	MD5STEP(F2, c, d, a, b, in[3] + 0xf4d50d87, 14);
+	MD5STEP(F2, b, c, d, a, in[8] + 0x455a14ed, 20);
+	MD5STEP(F2, a, b, c, d, in[13] + 0xa9e3e905, 5);
+	MD5STEP(F2, d, a, b, c, in[2] + 0xfcefa3f8, 9);
+	MD5STEP(F2, c, d, a, b, in[7] + 0x676f02d9, 14);
+	MD5STEP(F2, b, c, d, a, in[12] + 0x8d2a4c8a, 20);
+
+	MD5STEP(F3, a, b, c, d, in[5] + 0xfffa3942, 4);
+	MD5STEP(F3, d, a, b, c, in[8] + 0x8771f681, 11);
+	MD5STEP(F3, c, d, a, b, in[11] + 0x6d9d6122, 16);
+	MD5STEP(F3, b, c, d, a, in[14] + 0xfde5380c, 23);
+	MD5STEP(F3, a, b, c, d, in[1] + 0xa4beea44, 4);
+	MD5STEP(F3, d, a, b, c, in[4] + 0x4bdecfa9, 11);
+	MD5STEP(F3, c, d, a, b, in[7] + 0xf6bb4b60, 16);
+	MD5STEP(F3, b, c, d, a, in[10] + 0xbebfbc70, 23);
+	MD5STEP(F3, a, b, c, d, in[13] + 0x289b7ec6, 4);
+	MD5STEP(F3, d, a, b, c, in[0] + 0xeaa127fa, 11);
+	MD5STEP(F3, c, d, a, b, in[3] + 0xd4ef3085, 16);
+	MD5STEP(F3, b, c, d, a, in[6] + 0x04881d05, 23);
+	MD5STEP(F3, a, b, c, d, in[9] + 0xd9d4d039, 4);
+	MD5STEP(F3, d, a, b, c, in[12] + 0xe6db99e5, 11);
+	MD5STEP(F3, c, d, a, b, in[15] + 0x1fa27cf8, 16);
+	MD5STEP(F3, b, c, d, a, in[2] + 0xc4ac5665, 23);
+
+	MD5STEP(F4, a, b, c, d, in[0] + 0xf4292244, 6);
+	MD5STEP(F4, d, a, b, c, in[7] + 0x432aff97, 10);
+	MD5STEP(F4, c, d, a, b, in[14] + 0xab9423a7, 15);
+	MD5STEP(F4, b, c, d, a, in[5] + 0xfc93a039, 21);
+	MD5STEP(F4, a, b, c, d, in[12] + 0x655b59c3, 6);
+	MD5STEP(F4, d, a, b, c, in[3] + 0x8f0ccc92, 10);
+	MD5STEP(F4, c, d, a, b, in[10] + 0xffeff47d, 15);
+	MD5STEP(F4, b, c, d, a, in[1] + 0x85845dd1, 21);
+	MD5STEP(F4, a, b, c, d, in[8] + 0x6fa87e4f, 6);
+	MD5STEP(F4, d, a, b, c, in[15] + 0xfe2ce6e0, 10);
+	MD5STEP(F4, c, d, a, b, in[6] + 0xa3014314, 15);
+	MD5STEP(F4, b, c, d, a, in[13] + 0x4e0811a1, 21);
+	MD5STEP(F4, a, b, c, d, in[4] + 0xf7537e82, 6);
+	MD5STEP(F4, d, a, b, c, in[11] + 0xbd3af235, 10);
+	MD5STEP(F4, c, d, a, b, in[2] + 0x2ad7d2bb, 15);
+	MD5STEP(F4, b, c, d, a, in[9] + 0xeb86d391, 21);
+
+	state->h[0] += a;
+	state->h[1] += b;
+	state->h[2] += c;
+	state->h[3] += d;
+}
+
+static void md5_blocks(struct md5_block_state *state,
+		       const u8 *data, size_t nblocks)
+{
+	do {
+		md5_block(state, data);
+		data += MD5_BLOCK_SIZE;
+	} while (--nblocks);
+}
+
+void md5_init(struct md5_ctx *ctx)
+{
+	ctx->state = md5_iv;
+	ctx->bytecount = 0;
+}
+EXPORT_SYMBOL_GPL(md5_init);
+
+void md5_update(struct md5_ctx *ctx, const u8 *data, size_t len)
+{
+	size_t partial = ctx->bytecount % MD5_BLOCK_SIZE;
+
+	ctx->bytecount += len;
+
+	if (partial + len >= MD5_BLOCK_SIZE) {
+		size_t nblocks;
+
+		if (partial) {
+			size_t l = MD5_BLOCK_SIZE - partial;
+
+			memcpy(&ctx->buf[partial], data, l);
+			data += l;
+			len -= l;
+
+			md5_blocks(&ctx->state, ctx->buf, 1);
+		}
+
+		nblocks = len / MD5_BLOCK_SIZE;
+		len %= MD5_BLOCK_SIZE;
+
+		if (nblocks) {
+			md5_blocks(&ctx->state, data, nblocks);
+			data += nblocks * MD5_BLOCK_SIZE;
+		}
+		partial = 0;
+	}
+	if (len)
+		memcpy(&ctx->buf[partial], data, len);
+}
+EXPORT_SYMBOL_GPL(md5_update);
+
+static void __md5_final(struct md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE])
+{
+	u64 bitcount = ctx->bytecount << 3;
+	size_t partial = ctx->bytecount % MD5_BLOCK_SIZE;
+
+	ctx->buf[partial++] = 0x80;
+	if (partial > MD5_BLOCK_SIZE - 8) {
+		memset(&ctx->buf[partial], 0, MD5_BLOCK_SIZE - partial);
+		md5_blocks(&ctx->state, ctx->buf, 1);
+		partial = 0;
+	}
+	memset(&ctx->buf[partial], 0, MD5_BLOCK_SIZE - 8 - partial);
+	*(__le64 *)&ctx->buf[MD5_BLOCK_SIZE - 8] = cpu_to_le64(bitcount);
+	md5_blocks(&ctx->state, ctx->buf, 1);
+
+	cpu_to_le32_array(ctx->state.h, ARRAY_SIZE(ctx->state.h));
+	memcpy(out, ctx->state.h, MD5_DIGEST_SIZE);
+}
+
+void md5_final(struct md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE])
+{
+	__md5_final(ctx, out);
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+EXPORT_SYMBOL_GPL(md5_final);
+
+void md5(const u8 *data, size_t len, u8 out[MD5_DIGEST_SIZE])
+{
+	struct md5_ctx ctx;
+
+	md5_init(&ctx);
+	md5_update(&ctx, data, len);
+	md5_final(&ctx, out);
+}
+EXPORT_SYMBOL_GPL(md5);
+
+static void __hmac_md5_preparekey(struct md5_block_state *istate,
+				  struct md5_block_state *ostate,
+				  const u8 *raw_key, size_t raw_key_len)
+{
+	union {
+		u8 b[MD5_BLOCK_SIZE];
+		unsigned long w[MD5_BLOCK_SIZE / sizeof(unsigned long)];
+	} derived_key = { 0 };
+
+	if (unlikely(raw_key_len > MD5_BLOCK_SIZE))
+		md5(raw_key, raw_key_len, derived_key.b);
+	else
+		memcpy(derived_key.b, raw_key, raw_key_len);
+
+	for (size_t i = 0; i < ARRAY_SIZE(derived_key.w); i++)
+		derived_key.w[i] ^= REPEAT_BYTE(HMAC_IPAD_VALUE);
+	*istate = md5_iv;
+	md5_blocks(istate, derived_key.b, 1);
+
+	for (size_t i = 0; i < ARRAY_SIZE(derived_key.w); i++)
+		derived_key.w[i] ^= REPEAT_BYTE(HMAC_OPAD_VALUE ^
+						HMAC_IPAD_VALUE);
+	*ostate = md5_iv;
+	md5_blocks(ostate, derived_key.b, 1);
+
+	memzero_explicit(&derived_key, sizeof(derived_key));
+}
+
+void hmac_md5_preparekey(struct hmac_md5_key *key,
+			 const u8 *raw_key, size_t raw_key_len)
+{
+	__hmac_md5_preparekey(&key->istate, &key->ostate, raw_key, raw_key_len);
+}
+EXPORT_SYMBOL_GPL(hmac_md5_preparekey);
+
+void hmac_md5_init(struct hmac_md5_ctx *ctx, const struct hmac_md5_key *key)
+{
+	ctx->hash_ctx.state = key->istate;
+	ctx->hash_ctx.bytecount = MD5_BLOCK_SIZE;
+	ctx->ostate = key->ostate;
+}
+EXPORT_SYMBOL_GPL(hmac_md5_init);
+
+void hmac_md5_init_usingrawkey(struct hmac_md5_ctx *ctx,
+			       const u8 *raw_key, size_t raw_key_len)
+{
+	__hmac_md5_preparekey(&ctx->hash_ctx.state, &ctx->ostate,
+			      raw_key, raw_key_len);
+	ctx->hash_ctx.bytecount = MD5_BLOCK_SIZE;
+}
+EXPORT_SYMBOL_GPL(hmac_md5_init_usingrawkey);
+
+void hmac_md5_final(struct hmac_md5_ctx *ctx, u8 out[MD5_DIGEST_SIZE])
+{
+	/* Generate the padded input for the outer hash in ctx->hash_ctx.buf. */
+	__md5_final(&ctx->hash_ctx, ctx->hash_ctx.buf);
+	memset(&ctx->hash_ctx.buf[MD5_DIGEST_SIZE], 0,
+	       MD5_BLOCK_SIZE - MD5_DIGEST_SIZE);
+	ctx->hash_ctx.buf[MD5_DIGEST_SIZE] = 0x80;
+	*(__le64 *)&ctx->hash_ctx.buf[MD5_BLOCK_SIZE - 8] =
+		cpu_to_le64(8 * (MD5_BLOCK_SIZE + MD5_DIGEST_SIZE));
+
+	/* Compute the outer hash, which gives the HMAC value. */
+	md5_blocks(&ctx->ostate, ctx->hash_ctx.buf, 1);
+	cpu_to_le32_array(ctx->ostate.h, ARRAY_SIZE(ctx->ostate.h));
+	memcpy(out, ctx->ostate.h, MD5_DIGEST_SIZE);
+
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+EXPORT_SYMBOL_GPL(hmac_md5_final);
+
+void hmac_md5(const struct hmac_md5_key *key,
+	      const u8 *data, size_t data_len, u8 out[MD5_DIGEST_SIZE])
+{
+	struct hmac_md5_ctx ctx;
+
+	hmac_md5_init(&ctx, key);
+	hmac_md5_update(&ctx, data, data_len);
+	hmac_md5_final(&ctx, out);
+}
+EXPORT_SYMBOL_GPL(hmac_md5);
+
+void hmac_md5_usingrawkey(const u8 *raw_key, size_t raw_key_len,
+			  const u8 *data, size_t data_len,
+			  u8 out[MD5_DIGEST_SIZE])
+{
+	struct hmac_md5_ctx ctx;
+
+	hmac_md5_init_usingrawkey(&ctx, raw_key, raw_key_len);
+	hmac_md5_update(&ctx, data, data_len);
+	hmac_md5_final(&ctx, out);
+}
+EXPORT_SYMBOL_GPL(hmac_md5_usingrawkey);
+
+MODULE_DESCRIPTION("MD5 and HMAC-MD5 library functions");
+MODULE_LICENSE("GPL");